A grenade launcher mounted underneath a gun, most commonly an assault rifle, in Call of Duty games. The word "Noobtube" comes from the player using it being a "noob" and the fact that the grenade launcher looks like a tube; hence the word Noobtube. Noobtubes carry 2 grenades that can also be refilled using the Scavenger perk or the highly despised One Man Army perk. They have a very large blast radius and enormous damage, leading to one hit kills even if the grenade lands 10-15 from the enemy. The most hated thing you can do with the Noobtube, is to join a domination game and shoot the Noobtube across the map at the beginning of the game into the enemies flag closest to their spawn, earning a 2-6 hit kill with one shot. The players using the Noobtube are called Noobtubers and are hated by many players in the gaming community because of the weapon requiring little effort to get kills with because of its high damage and blast radius. A Noobtubers K/D is usually quite high and they commonly achieve higher ranked killstreaks, (Pave low, Chopper gunner, AC-130, ect).

(Immature enemy)
Noobtuber kills enemy-
Enemy: OMG! Learn how to use a gun you dumb faggot Noobtuber!
Noobtuber: I'm just trying to play the objective and get kills, chill!
Enemy: (rage quits and joins a new game)
(Mature enemy)
Noobtuber kills enemy-
Enemy: (grunts in annoyance) that Noobtube is annoying but is is a weapon in the game and he is allowed to use it.
Noobtuber: Thank you! Someone understands! Want to be my friend?

The biggest fag you will ever meet in a online match. A fag that uses a grenade launcher the whole game and always kills you on a kill streak. Usually uses danger close and a claymore; and always camps :{